An imaging system of the aforementioned type is known from document EP 2,122,326 B1. The imaging system comprises a light source suitable for illuminating a sample and a CCD sensor able to acquire at least one image of the illuminated sample. The light source includes a light-emitting diode with an opening diameter equal to 60 μm, or a light-emitting diode with a large zone associated with a diaphragm, also called pinhole, having a diameter equal to 6 μm. The observed diffraction patterns then include a center and one or several concentric rings positioned around the center.
However, the diffraction patterns observed with such an imaging system are not optimal; in particular, when the surface of the diode is too large, the diaphragm projects the image of the electrode(s) making up the light-emitting diode on the sensor. Thus, when no sample is present, the image collected on the sensor is not homogenous.
This effect occurs in the presence of a sample, which is detrimental to the quality of the obtained images.